Different types of Metal Oxide Semiconductor (MOS) transistors can be fabricated and used in electronic circuits. For example, thick-gate and thin-gate transistors could be used in electronic circuits, where the thick-gate and thin-gate transistors have gate oxide layers of different thicknesses. As another example, standard, native, and depletion n-channel MOS (NMOS) transistors could be used in electronic circuits. A standard NMOS transistor is typically formed within a p-well, a native NMOS transistor is typically formed directly on a semiconductor substrate, and a depletion NMOS transistor is typically formed within a p-well that has a special depletion implant in the gate region of the transistor.
The different types of transistors typically have different operating characteristics. For example, a gate-to-source voltage (VGS) at or near zero volts may be needed to turn off a thick-gate standard NMOS transistor, a gate-to-source voltage of −300 millivolts may be needed to turn off a thick-gate native NMOS transistor, and a gate-to-source voltage of −500 to −600 millivolts may be needed to turn off a thick-gate depletion NMOS transistor. In certain circuits, this means that native and depletion NMOS transistors cannot be turned completely off, such as when a source voltage rail (VDD) is 1.8 volts and a ground voltage rail (VSS) is zero volts. The inability to completely turn off native and depletion NMOS transistors often prevents the native and depletion NMOS transistors from being used in standard logic gates and other circuits.